Underground antenna buried in frozen soil



Jan- 31,1967 "DARCY A. SHOCK ETAL 3,302,206

UNDERGROUND ANTENNA lBURIED IN FROZEN SOIL Filed Jan. 2l, 1965 2Sheets-Sheet l FILL' E74- INVENTORS D. A. 5Hocl Jan. 31, l967 D'ARCY A.SHOCK ETAL 3,302,206

UNDERGROUND ANTENNA BURED IN FROZEN SOIL 2 Sheets-Sheet 2 Filed Jan. 2l,1963 Tl E7-5' NVENTQRS 0 A. SHOCK,

W, www f' BYl H F- CoFFE-Q Mfg/V United States Patent C 3,302,206UNDERGROUND ANTENNA BURIED IN FROZEN SOIL DArcy A. Shock, Warren W.Woods, vand Henry F. Colfer, Ponca City, Okla., assignors to ContinentalOil Company, Ponca City, Okla., a corporation of Dela- Ware Filed Jan.21, 1963, Ser. No. 252,755 3 Claims. (Cl. 343-719) The present inventionrelates to method and -apparatus for electrically insulating a buriedconductor and more particularly, but not by way of limitation, relatesto a novel radio antenna and method for constructing same.

As is well known, so-called hard7 military bases, such as missile sites,which are considered invulnerable to anything but a direct hit :by anatomic warhead, are presently bein-g designed and constructed.`Invulnerability is most commonly achieved by placing vall essentialstructures below ground level s-o that they will escape the tremendousblast `forces as well as the radiation effects of heat and at-omicparticles which may be caused by a near-miss. The construction of such asite is complicated by the fact that every military installation dependsheavily upon a communications system. Laying of underground cables andtelephone lines over the vast distances required for proper deploymento-f the military installati-ons would be prohibitive in cost. Therefore,it is essential that some type of radio communications system beprovided which can be entirely buried, including the antenna. One typeof radio communications system which is especially well adapted for thistype of installation utilizes an antenna comprised of a plurality ofelectrical conductors buried several feet below the surface of the earthand arrayed in some suitable pattern covering an area of severalth-o-usand feet square, depending upon the parti-cular frequency beingused. In the operation of this radio equipment, it is important that theburied conductors of the antenna be essentially insulated from thesurrounding soil and that the conductance of the soil surrounding theantenna be maintained substantially constant at the low conductancevalue. Almost all soils are highly conductive when moist because themoisture normally becomes saline as a result of dissolved salts andminerals which produce a highly conductive ionic solution. The problemis further complicated by the fact that as the moisture content of thesoil varies from period to period or season to season, the conductivityof the soil also varies s-o as to sometime interfere with theadjustments of the c-ommunicati-ons systems.

Therefore, it is an important object of the present invention to reducethe electrical conductance of the soil around a buried electricalconductor, such as an antenna, to a minimum and to maintain the minimumconductance substantially constant.

Another object of the present invention is toA provide a microwaveantenna which is materially protected yfrom destruction by enemy attack.

Still another object of the present invention is to provide a method.for constructing a microwave antenna of the type described.

Many additional objects and advantages of the present invention will Ibeevident to those skilled in the art from the following detaileddescription `and drawings, where- FIG. 1 is a vertical sectional view,somewhat schematic, of an antenna constructed in accordance with thepresent invention;

FIG. 2 is a plan view, somewhat schematic, of the device of FIG. 1;

FIG. 3 is a sectional view, somewhat schematic, which ice se-rves toillustrate a portion of the structure of the device of FIG. l; and,

FIG. 4' is a graph sh-owing the conductance of a typical saline soilplotted against temperature.

Referring now to the drawings, and in particular to FIGS. 1 and 2, lanantenna constructed in accordance with the present invention isdesignated generally by the reference numeral 10. The antenna 10comprises a plurality lof conductors 12 which are buried in andtherefore sur-rounded by soil 14. The conductors 12 may be arrayed inthe most suitable pattern for maxi-mum electromagnetic propagation landreception, the particular optimum pattern being dependent .upon thefrequency and design of the particular radio communications system f-orwhich the conductors 12 form the antenna in accordance with designconsiderations which are well |known in the art. However, for purposesof this disclosure, it -is sufficient to note that the conductors 12 arearrayed within the general confines of the dotted outline 16 as shown inFIG. 2.

The soil 14 may be virtually any soil, and will in most cases 'be thenative soil of the particular locality. Most native soils havesufficient moisture to be readily frozen but in some instances it may bedesirable to add some moisture so that the soil can Ibe more easilyfrozen at low temperatures. The moisture within the soil will invariablybe saline at least to a certain extent due to dissolved salts andminerals and accordingly the .soil would normally have a relatively highspeci-lic conductance. However, in accordance with the presentinvention, the temperature of soil 14 is reduced until the area aro-undantenna 10 is substantially completely Ifrozen and the ionic salts andminerals within the s-olution are immobilized and the soil madeessentially nonconductive. FIGURE 4 is a -graiph showing'the specifi-cconductance of a saturated NaCl solution plotted against temperature. Itwill be noted that the specific conductance decreases linearly as theternperature is lowered from 0 C. to 30 C. and that the slope of .theplot is such that by simple extrapolation it would appear that theconductance of the solution could not belowered t-o a signicant valuewithout reducing the temperature to a completely impractical value.However, we have discovered that -by reducing the temperature further,the speciiic conductance begins t-o be reduced at a much greater ratebel-ow approximately 40 C. Such that at attainable temperatures thespecic conductance of a salt solution and therefore of a moisture ladensoil can 'be reduced to a very small value and the total conductance ofthe soil around the electrical conductors 12 reduced to susbtantiallyzero, assuming that a reasonably large thickness of the frozen soil isavailable for insulation purposes. Therefore it is to be understood thatin the antenna installation 10 the soil 14 is at a temperaturelsuliiciently low as to have the desired low conductance value, orconversely, the desired high insulation value. The particulartemperature necessary -f-or a specific antenna installation will vary tosome degree Ifrom location to location but can 'be determined at eachsite merely by lowering the temperature 'of the soil and measuring thespecic conductance so as togobtain a graph as shown in F-IG. 4, and thencomputing, by normal engineering methods, the necessary temperature yandthickness of frozen soil required to attain the desi-red level ofinsulation.

A suitable refrigeration means, indicated generally by the referencenumeral 18, is provided to freeze and maintain the soil 14 at the lowtemperature. The refrigeration means 18 may be comprised of any suitablerefrigeration system and does not per se comprise a part of the presentinvention. One type of refrigeration system which has been successfullyused for freezing the earth in other appli-cations utilizes theexpansion of a liquefied refrigerant such as propane. The propane may bemechanically compressed by suitable compressor apparatus representedschematically and designated by the reference numeral 20. The compressedpropane may then be circulated sequentially through a series ofrefrigerator pilings 22 by suitable interconnecting conduits 24 andexpanded to produce cooling. Each refrigerator piling 22 is comprisedessentially of an external casing 26 and an inner conduit 28 whichextends to a point adjacent to the bottom of the casing. The inletconduit 24 for passing the refrigerant into each refrigerator piling 22is connected to the inner conduit 28. The next successive conduit 24which serves as an outlet for the particular refrigerator piling isconnected to the upper end of the casing 26 at an outlet point 30 and isthen connected to the inner conduit 28 of the next succeedingrefrigerator piling 22, as best seen in FIG. 3 wherein like componentsof each of the refrigerator pilings 22 are indicated by the samereference numerals.

Therefore, referring once again to FIG. 2, the refrigerant is circulatedfrom the apparatus 20 successively through the refrigerator pilings22-22p in alphabetical se. quence and thereby continually maintains thesoil 14 frozen both above and below the conductors 12 and for aconsiderable distance around the periphery of the electrical conductors12 which, as previously mentioned, are arrayed within the confines ofthe dotted outline 116 of FIG. 2 in order to lower the conductance ofthe soil to a minimum value. It will be noted that the refrigeratorpilings 22 extend to a substantial depth below the conductors 12 as bestseen in FIG. 1, so as to freeze the soil to a considerable depth andthereby reduce heat transfer from the surrounding earth formation due tothe fact that the frozen earth is a good thermal insulator. In order toprevent heat transfer from the atmosphere into the frozen soil 14, alayer of expanded perlite 34 may cover the entire area over which thesoil 14 is frozen. A water impervious film 38, such as asphalt or asuitable plastic, may then be placed over the perlite insulation both totrap a quantity of dead air space within the expanded perlite and toprevent the intrusion of surface water into the zone of frozen soil. Inthe absence of camouflage requirements, the water impervious film 38 isprefer-ably covered with a white or heat reflecting layer of material 40which may be chipped white rock, or a suitable silvered coating on thewater impervious film 38.

One method by which the antenna installation may be constructed inaccordance with the method of the present invention is as follows. Theconductors 12 of the antenna proper are imbeded in the earth in thedesired array by any suitable means such as by ditching and backcovering. A number of vertical bores are drilled in the soil 14 forreceiving the refrigerator pilings 22. The bores may be drilled in anysuitable pattern but preferably are drilled in some predetermined andorganized pattern such as is illustrated in FIG. 2 wherein the bores arerepresented by the dotted circles 44. A plurality of refrigeratorpilings 22 may then be inserted in the two center rows A and B of boreholes 44 and interconnected by suitable conduits 24 as represented bythe dotted lines 46. The refrigerant is then circulated through theconduit 24 and the refrigerator pilings 22 disposed in the well -boresof rows A and B until the soil 14 is lowered to the desired temperature.After the temperature of the soil between an@ t9 a distan@ '91.1 aaahsid@ of the rows A and B has CFI been lowered to the desired value, therefrigerator pilings 22 are withdrawn from the bore holes and are moivedto the bore holes of rows C and D. The conduits 24 are again connectedas previously described along the dotted lines 48 and the refrigerationprocess repeated. It will be noted that four more refrigerator pilings22 are required for this step. After the soil 14 has been lowered to thedesired temperature, the center four pilings on the two sides arewithdrawn from the respective well bores 44 and moved outwardly to thewell bores 44 in rows E and F. All refrigerator pilings 22 will then bein the permanent positions for the completed antenna installation. Theconduits 24 are then permanently connected between the severalrefrigerator pilings and the final outside ring of the soil 14 loweredto the desired temperature. Of course, during the several steps offreezing the soil in rings, the soil in the center is maintained at the`desired low temperature.

As the refrigerator pilings 22 are withdrawn from the innermost wellbores 44, the well bores are filled with soil or with a suitableinsulating material such as expanded perlite. The layer of insulatingmaterial 34 is spread over the entire installation and then covered withthe suitable moistureproof film 38 of plastic or asphalt either beforeor after the freezing steps. The layer of refiecting chips or othersurface may be similarly applied if required. Continued operation of therefrigeration device with the refrigerator pilings 22 in the desiredpositions maintains the soil 14 within the boundaries defined by theoutline 36 at the desired low temperature. The insulation of the eartharound the block of frozen soil and the insulation applied to thesurface serve to substantially reduce the heat exchange with latmosphereand the earth.

We claim:

l. An antenna installation comprising:

a quantity of soil at a temperature below about a plurality ofinterconnected freeze points arranged in a closed pattern surroundingIat least a portion of said soil, for maintaining said soil at atemperature below about 30 C., means communicating with said freezepoints for furnishing refrigerant thereto at a temperature below 30 C.,and

a plurality of horizont-ally disposed conductors embedded in said soilat a position within said closed pattern of freeze points and below thesurface of said soil.

2. The antenna defined in claim 1 further characterized by a quantity ofheat insulating material overlying said conductors.

3. The antenna defined in claim 2 further characterized by awater-impervious film overlying said heat insulating material.

References Cited by the Examiner UNITED STATES PATENTS 1,530,129 3/1925Loftin et al 343-719 3,183,510 5/1965 Rawls 343-719 3,216,016 11/1965Tanner 343-719 FOREIGN PATENTS 5,535 5/1914 Great Britain.

ELI LIEBERMAN, Primary Examiner. W. K, TAYLOR, Assistant Examinar,

1. AN ANTENNA INSTALLATION COMPRISING: A QUANTITY OF SOIL AT ATEMPERATURE BELOW ABOUT -30*C., A PLURALITY OF INTERCONNECTED FREEZEPOINTS ARRANGED IN A CLOSED PATTERN SURROUNDING AT LEAST A PORTION OFSAID SOIL, FOR MAINTAINING SAID SOIL AT A TEMPERATURE BELOW ABOUT -30*C., MEANS COMMUNICATING WITH SAID FREEZE POINTS FOR FURNISHINGREFRIGERANT THERETO AT A TEMPERATURE BELOW -30*C., AND A PLURALITY OFHORIZONTALLY DISPOSED CONDUCTORS EMBEDDED IN SAID SOIL AT A POSITIONWITHIN SAID CLOSED PATTERN OF FREEZE POINTS AND BELOW THE SURFACE OFSAID SOIL.